The overall goal of this SCCOR proposal is to elucidate the roles of innate and adaptive immunity in the pathogenesis of chronic lung disease. The SCCOR proposal consists of four interrelated research projects that are focused on two chronic lung diseases: asthma and bronchiolitis obliterans syndrome (BOS) with a common underlying theme of epithelial injury, inflammation, repair and fibroproliferation. The central hypothesis to be tested is that chronic lung disease occurs as a consequence of destructive or maladaptive host responses to common environmental insults that challenge the lung. The fundamental roles of innate and adaptive host responses are to recognize invading antigens, pathogens or altered self components with the purpose of eradicating the offending agents and restoring tissue integrity. While resolution can occur when the host response is normal, an exogenous insult cannot be contained when a critical host factor is inactivated, dysregulated, or becomes dysfunctional. Such maladaptive host responses lead to chronic lung disease. The project specific hypotheses within this SCCOR proposal are: Project 1: Surfactant proteins SP-A and SP-D, which are produced by both alveolar and airway cells, interact with cells of both the adaptive and innate immune systems to coordinately maximize defense against inhaled allergens and that cause and exacerbate asthma, while minimizing an over exuberant immune response that could result in inflammation, tissue damage and chronic lung disease. Project 2: Interleukin 13 (IL-13) modulates airway fibroblast function in human asthma via increased expression of platelet-derived growth factor (PDGF), an adaptive host response, and subsequent airway remodeling via fibroblast proliferation, collagen expression and decreased elastin expression. Project 3: Activation of innate immunity through toll like receptors (TLRs) in the transplanted lung promotes the adaptive alloimmune response leading to acute rejection and BOS. Project 4: Innate immune mechanisms regulate chronic inflammation and tissue remodeling and specifically, host hyaluronan and TLR interactions are critical components of the injury and repair response in non-infectious lung injury, BOS and chronic asthma. These studies will contribute to our understanding of normal and altered host responses on lung structure and function and will provide a basis for investigation and development of new therapies for the treatment of chronic lung diseases.